Abstract of Proposed Research: I. The objective of this reseach proposal is to examine the responsiveness of the rat uterus during the period of reproductive decline. The experiments are divided into two major areas. Firstly, the induction of two uterine enzymes glucose-phosphate dehydrogenase (G6PD) and ornithine decarboxylase (OCD) after hormonal stimulation or induction of deciduomata will be examined for a faulty or delayed response. Secondly, the effect of increasing age on the concentration of "altered" proteins will be examined. II. Methodology: l. The kinetics of induction (lag time before increase, rate of increase, and maximal levels attained) of uterine G6PD and ODC after estradiol administration will be determined. 2. The levels of the uterine enzymes during the hormonal preparation for the decidual response will be compared in young and old animals. 3. The kinetics of uterine ODC and G6PD induction will be determined in rats which have been stimulated to form deciduomata. 4. The presence of altered enzymes in senescent uteri will be determined using differential heat stability of the enzyme and comparative immuno-titration.